Do fishing loot tables change while fiishing from the same spot?

I am 90% sure this is an actual mechanic in the game. Every time I level fishing on an alt, I notice it. The drop rates for Oily Blackmouths, Firefins and Rainbows start out as expected (25%, 15%, 55%) but after 10, 20, 30 min etc it becomes noticably different. I start catching Firefins more frequently and Oily Blackmouth drop rate eventually disappears entirely as I catch 20+ Rainbowfins in a row.

So when I see this happening, I fly from Wetlands to Hillsbrad Foothills and start fishing there. That flight seems to reset it and I start catching Oily Blackmouths again at the expected rate of 25% per cast.

I don't see anything in the public code to that effect. Unless it's a custom warmane change, what you are seeing is the result of your bad luck.